/** 图片压缩，默认同比例压缩
 *  @param {Object} fileObj
 *  图片对象
 *  回调函数有一个参数，base64的字符串数据
 */
export function compress(fileObj, callback) {
      try {
        const image = new Image()
        image.src = URL.createObjectURL(fileObj)
        image.onload = function() {
          const that = this
          // 默认按比例压缩
          let w = that.width
          let h = that.height
          const scale = w / h
          w = fileObj.width || w
          h = fileObj.height || (w / scale)
          let quality = 0.7 // 默认图片质量为0.7
          // 生成canvas
          const canvas = document.createElement('canvas')
          const ctx = canvas.getContext('2d')
          // 创建属性节点
          const anw = document.createAttribute('width')
          anw.nodeValue = w
          const anh = document.createAttribute('height')
          anh.nodeValue = h
          canvas.setAttributeNode(anw)
          canvas.setAttributeNode(anh)
          ctx.drawImage(that, 0, 0, w, h)
          // 图像质量
          if (fileObj.quality && fileObj.quality <= 1 && fileObj.quality > 0) {
            quality = fileObj.quality
          }
          // quality值越小，所绘制出的图像越模糊
          const data = canvas.toDataURL('image/jpeg', quality)
          // 压缩完成执行回调
          const newFile = convertBase64UrlToBlob(data)
          callback(newFile)
        }
      } catch (e) {
        console.log('压缩失败!')
      }
    }
    function convertBase64UrlToBlob(urlData) {
      const bytes = window.atob(urlData.split(',')[1]) // 去掉url的头，并转换为byte
      // 处理异常,将ascii码小于0的转换为大于0
      const ab = new ArrayBuffer(bytes.length)
      const ia = new Uint8Array(ab)
      for (let i = 0; i < bytes.length; i++) {
        ia[i] = bytes.charCodeAt(i)
      }
      return new Blob([ab], { type: 'image/png' })
    }